During the last year we have determined the nucleotide sequence of: 1) the long terminal repeats of integrated M-MLV, integrated AKR, and unintegrated M-MLV and M-MSV, 2) the viral src gene and its cellular homologue, 3) the junction between viral and cellular src gene, 4) the portions of gag, pol, and env gene of M-MLV and M-MSV, and 5) we have used purified AMV reverse transcriptase for synthesis of double-stranded viral DNA from purified virions of M-MLV. Such double-stranded DNA molecules were molecularly cloned in plasmids. Five M-MLV specific plasmids were identified. Our future goals are to: 1) continue nucleotide sequence analysis of the viral gene, 2) use reverse transcriptase for creating site-directed mtagenesis in vitro, and 3) identify the pol gene product in the infected cell by raising antisera to peptide synthesized from nucleotide sequence analysis.